1. Field of the Invention
The present invention relates to an optical modulation element and a projection display device. More particularly, the present invention relates to a layout structure of optical elements on the periphery of an optical modulation element that modulates a light flux according to image information.
2. Description of Related Art
A projection display device basically consists of a light source lamp unit, an optical unit for optically processing a light flux emitted from the light source lamp unit so as to synthesize a color image corresponding to image information, a projection lens unit for enlarging and projecting the synthesized light flux onto a screen, a power supply unit, and a circuit substrate on which a control circuit and the like are mounted.
FIGS. 17(A)-(C) schematically show the construction of the optical unit and the projection lens unit of the above-mentioned components. As shown in this drawing, an optical system of an optical unit 9a includes a lamp body 81 serving as a light source, a color separation optical system 924 for separating a light flux W emitted from the lamp body 81 into respective color light fluxes R, G and B of the primary colors of red (R), green (G) and blue (B), three sheets of liquid crystal modulation elements 925R, 925G and 925B for modulating the separated respective color light fluxes according to image information, and a color synthesizing prism 910 in the shape of a prism with a square cross section to synthesize the modulated color light fluxes. The light flux W emitted from the lamp body 81 is separated into respective color light fluxes R, G and B by the color separation optical system 924 including various types of dichroic mirrors, and the red and green light fluxes R and G of the respective color light fluxes are emitted from outgoing sections provided in the color separation optical system 924 towards corresponding liquid crystal modulation elements 925R and 925G. The blue light flux B is guided to the corresponding liquid crystal modulation element 925B via a light guide system 927, and is emitted from an outgoing section provided in the light guide system 927 towards the corresponding liquid crystal modulation element 925B.
As shown in FIGS. 17(B) and 17(C) in enlargement, in the optical unit 9a, polarizers 960R, 960G and 960B are respectively arranged on the side of incident surfaces of the liquid crystal modulation elements 925R, 925G and 925B so that they unify the planes of polarization of the respective color light fluxes to be incident on the liquid crystal modulation elements 925R, 925G and 925B. In addition, polarizers 961R, 961G and 961B are respectively arranged on the side of outgoing surfaces of the liquid crystal modulation elements 925R, 925G and 925B so that they unify the planes of polarization of the modulated color fluxes to be incident on the color synthesizing prism 910. The actions of these polarizers allow an enlarged image excellent in contrast to be projected onto the surface of a screen 10. Of the two polarizers that sandwich the liquid crystal modulation elements 925R, 925G and 925B, the polarizers 961R, 961G and 961B positioned on the side of the outgoing surfaces of the liquid crystal modulation elements 925R, 925G and 925B are bonded to the light outgoing surfaces of the liquid crystal modulation elements.
Incidentally, as the liquid crystal modulation elements 925R, 925G and 925B, an active matrix-type liquid crystal device is generally used, in which pixels arranged in the form of a matrix are controlled by a switching element.
Here, in order to improve the contrast of an image enlarged and projected onto the screen 10, it is effective to bond a polarizer, which has high selection properties with respect to polarized light, to the light outgoing surface of each of the liquid crystal modulation elements 925R, 925G and 925B. However, such a polarizer having high selection properties absorbs much light and therefore, generates much heat. Inside the projection display device mentioned above, an air flow is formed as shown in FIG. 17(C) and cools the polarizer. However, since the polarizer is directly attached to the light outgoing surface of the liquid crystal modulation element, heat is apt to be transmitted to the liquid crystal modulation element, and to thereby increase the temperature of the liquid crystal modulation element. This increase in temperature deteriorates the optical properties of a liquid crystal panel, and the image contrast.
Thus, it may be possible to arrange the polarizer apart from the light outgoing surface of the liquid crystal modulation element. However, if the polarizer is simply arranged apart from the light outgoing surface, there is a fear that the switching element in the liquid crystal modulation element may malfunction due to a light beam reflected by the light outgoing surface of the liquid crystal modulation element. In addition, there is a fear that dust or the like may be caused by an air flow formed inside the projection display device to adhere to the light outgoing surface of the liquid crystal modulation element, and it may make high-quality image projection impossible.
In view of the above-described points, an object of the present invention is to provide an optical modulation element and a projection display device that achieve high-quality image projection by preventing dust from adhering to the light outgoing surface of the optical modulation element without deteriorating the switching characteristic of the optical modulation element.
In order to achieve the above-described object, there is provided an optical modulation element for modulating a light flux emitted from a light source according to image information, wherein a transparent plate is provided on at least one surface thereof, and the space between the transparent plate and the optical modulation element is shielded from the outside by a dust-preventing member.
In such an optical modulation element, heat generated by a polarizer to be transmitted to the optical modulation element can be further reduced. In addition, since the space between the transparent plate and the optical modulation element is shielded from the outside by the dust-preventing member, dust does not enter the space. For this reason, negative effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be solved.
The dust-preventing member may preferably be formed of resin containing glass fiber. In this case, it is possible to restrict linear expansion, to prevent movement of the optical modulation element, and to maintain a constant temperature and a uniform in-plane temperature distribution of the optical modulation element.
On the other hand, the dust-preventing member may be made of metal. This makes it possible to improve the heat dissipation effect. In particular, when a polarizer is bonded to the transparent plate, it is preferable that the dust-preventing member be made of metal because heat is generated with the absorption of light by the polarizer.
In the optical modulation element of the present invention, it is also possible to bond the polarizer to the transparent plate. This prevents dust from entering between the polarizer and the transparent plate. For this reason, negative effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be prevented more effectively.
In addition, in the optical modulation element of the present invention, at least one surface of the transparent plate may preferably be coated with a surface-active agent, or treated for electrostatic protection. This makes it possible to prevent dust from adhering to the transparent plate.
A projection display device of the present invention may be constructed in which a transparent plate is provided on the side of a light outgoing surface of the optical modulation element, and the space between the transparent plate and the light outgoing surface of the optical modulation element is shielded from the outside by a dust-preventing member.
When the polarizer is arranged on the side of the light outgoing surface of the transparent plate, since the transparent plate and an air layer exist between the optical modulation element and the polarizer, heat generated by a polarizer to be transmitted to the optical modulation element can be further reduced. In addition, since the space between the transparent plate and the optical modulation element is shielded from the outside by the dust-preventing member, dust does not enter the space. For this reason, bad effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be solved.
As the dust-preventing member, a member having a frame body for holding the optical modulation element and the transparent plate, and a light outgoing-side outer frame detachably fixed to the light outgoing side of the frame body may be used. In the case of using such a dust-preventing member, the frame body may be provided with a light incident contact surface which contacts a part of the light incident surface of the optical modulation element, an optical modulation element side contact surface which contacts the side surface of the optical modulation element, and a transparent plate side contact surface which contacts the side surface of the transparent plate. In addition, the light outgoing-side outer frame may be provided with a pressure surface that can press a part of the light outgoing surface of the transparent plate towards the frame body.
This allows the optical modulation element to come into contact with the light incident contact surface and the optical modulation element contact surface provided on the frame body, thereby being arranged in a predetermined position on the frame body. In addition, the position of the transparent plate relative to the frame body and the optical modulation element is defined by the transparent plate contact surface and a spacer provided on the frame body. Therefore, if the light outgoing-side outer frame, is fixed to the frame body after the optical modulation element, spacer and transparent plate have been superposed in this order, the light outgoing surface of the transparent plate is pressed by the pressure surface of the light outgoing-side outer frame towards the frame body side, so that the optical modulation element, spacer and transparent plate can be held by the frame body and the light outgoing-side outer frame, and at the same time, arrangement thereof in relation to one another can be maintained.
If the optical modulation element, the transparent plate and the like are fixed to the frame body using an adhesive, replacement thereof requires much labor. For example, after the optical modulation element and the transparent plate are separated from the frame body, a step of cleaning the adhesive adhering thereto is required.
In contrast, if the dust-preventing member such as described above is used, the light outgoing-side outer frame may merely be removed at the time of replacement of components, so that operability of rework can be improved.
It is desirable that a guide surface for putting a roller on the light outgoing surface of the optical modulation element and moving the roller in one direction is provided on the frame body. An antireflection film (AR film) may be bonded to the light outgoing surface of the optical modulation element for the purpose of improving the light utilizing efficiency. In such a case, if the roller is moved along the guide surface with the AR film placed on the light outgoing surface of the optical modulation element, the AR film can be easily bonded to the light outgoing surface of the optical modulation element.
In addition, since the guide surface is formed and the roller can be easily moved, it is easy to eliminate air bubbles generated between the light outgoing surface of the optical modulation element and the AR film. When replacing the AR film to which dust is adhered, the light outgoing-side outer frame is removed from the frame body and the transparent plate and the spacer are removed from the frame body. Thereafter, the AR film to which dust is adhered is separated from the light outgoing surface of the optical modulation element, and a new AR film is bonded with the use of the guide surface as described above while moving the roller. After the renewal of the AR film, the spacer and the transparent plate are superposed on the optical modulation element and the light outgoing-side outer frame is fixed to the frame body. The AR film can be easily renewed by using the dust-preventing member having the frame body on which the guide surface is formed.
In such a projection display device of the present invention, at least one surface of the transparent plate may be coated with an antireflection film, whereby light reflected from the transparent plate to the optical modulation element can be eliminated as described above, and switching characteristic of the optical modulation element can be maintained more excellently.
As the optical modulation element, either of transmissive or reflective optical modulation element may be used. When the transmissive optical modulation element is used, the transparent plate (light incident-side transparent plate) may desirably be provided not only on the side of the light outgoing surface, but also on the side of the light incident surface thereof and further, the space between the transparent plate provided on the side of the light incident surface and the light incident surface of the optical modulation element may desirably be shielded from the outside by the dust-preventing member.
When the transmissive optical modulation element is used and the transparent plate is provided on the side of the light incident surface thereof, a bonded light outgoing surface contacting a part of the light outgoing surface of the transparent plate on the side of the light incident surface and a transparent side contact surface contacting the side surface of the light incident-side transparent plate may be provided on the frame body of the dust-preventing member. In addition, a light incident-side outer frame detachably fixed to the light incident side of the frame body may be provided, and a pressure surface that can press the light incident surface of the light incident-side transparent plate towards the frame body may be provided on the light incident-side outer frame. This allows the light incident-side transparent plate to be held on the side of the light incident surface of the optical modulation element without using an adhesive. In addition, the transparent plate can be easily replaced by only removing the light incident-side outer frame from the frame body.
When the light incident-side outer frame and the light outgoing-side outer frame are formed of the same shape, engaging pawls extending along the side surface of the frame body are formed on the respective outer frames, and engaging projections each corresponding to the engaging pawls are formed on the frame body, the positions of the respective engaging projections formed on the frame body may desirably be shifted in the direction perpendicular to the thickness direction of the frame body. It is difficult to form a frame body on which the positions of the respective engaging projections match in the thickness direction of the frame body by upper and lower dies. However, the frame body can be easily formed as in a conventional manner by using the frame body as described above. In addition, since the light incident-side outer frame and the light outgoing-side outer frame have the same shape, commonality of components can be achieved.
The dust-preventing member may preferably be formed of resin containing glass fiber. In this case, it is possible to restrict linear expansion, to prevent movement of the optical modulation element, and to maintain a constant temperature and a uniform in-plane temperature distribution of the optical modulation element.
On the other hand, if the dust-preventing member is made of metal, it is possible to improve the heat dissipation effect. In particular, when a polarizer is bonded to the transparent plate, it is preferable that a mounting frame plate be made of metal because heat is generated with the absorption of light by the polarizer.
In the above-described projection display device of the present invention, it is also possible to bond the polarizer to the transparent plate. This prevents dust from entering between the polarizer and the transparent plate. For this reason, negative effects, such as the light flux emitted from the optical modulation element being scattered by dust, can be prevented more effectively.
In addition, in the above-described projection display device of the present invention, at least one surface of the transparent plate may preferably be coated with a surface-active agent, or treated for electrostatic protection. This makes it possible to prevent dust from adhering to the transparent plate.
Furthermore, the projection display device of the present invention adopts a construction such as a projection display device for separating a light flux emitted from a light source into a plurality of color light fluxes, modulating respective color light fluxes according to image information through an optical modulation element, synthesizing respective color light fluxes modulated by the optical modulation element by a color synthesizing means, and enlarging and projecting light synthesized by the color synthesizing means onto a projection surface through projection means, the projection display device including: a transparent plate provided on the side of a light outgoing surface of the optical modulation element, a dust-preventing member for holding the transparent plate and the optical modulation element and for shielding the space between the transparent plate and the light outgoing surface of the optical modulation element from the outside, a fixed frame plate fixed on the light incident surface of the color synthesizing means, and an intermediate frame plate removably fixed to the fixed frame plate, wherein the dust-preventing member is fixed to the intermediate frame plate. By the projection display device having this construction, the heat generated by the polarizer to be transmitted to the optical modulation element can be further reduced, and bad effects such that the light flux emitted from the optical modulation element is scattered by dust can be avoided. In addition to this, since it is not necessary to mount the optical modulation element to the color synthesizing means side by directly touching the optical modulation element, it is also possible to prevent the optical modulation element from interfering with other parts and to prevent it from being broken or chipped.
In the projection display device of the present invention having this construction, it is convenient to provide positioning means for positioning the optical modulation element by defining the mounting position of the dust-preventing member because the mounting positions of the dust-preventing member and the optical modulation element can be defined at the same time by this positioning means.
In the projection display device having this construction, when the transmissive optical modulation element is used, it is desirable to provide the transparent plate not only on the side of the light outgoing surface but also on the side of the light incident surface, as mentioned above. It is also desirable that the space between the transparent plate provided on the light incident surface side and the light incident surface of the optical modulation element is shielded from the outside by the dust-preventing member.
Here, there may be a case where the polarizer is fixed to the light incident surface of the color synthesizing means. In such a case, if the peripheral portion of the polarizer is completely superposed on the bonded surface of the fixed frame plate, there is a fear that the bonding strength decreases or the polarizer is separated. In order to assuredly avoid such a problem, it may be preferable to form the fixed frame plate so that only a part of the bonded surface is superposed on the peripheral portion of the polarizer. That is, it may be preferable that the bonded surface of the fixed frame plate to the light incident surface is not completely covered with the polarizer.
The surface of the transparent plate may be coated with a surface-active agent, or treated for electrostatic protection. In this case, it is difficult for dust to adhere to the surface of the transparent plate, and it is possible to prevent dust from adhering effectively.
When a polarizer is bonded to the transparent plate, since it is possible to prevent dust from entering between the optical modulation element and the polarizer, the polarization condition of light is not disturbed by dust. In addition, when a black image is displayed, a spot on the black image corresponding to the adhering dust can be prevented from being displayed as a white blank, and display quality can be improved.
When the above-described dust-preventing member is formed of resin containing glass fiber, it is possible to restrict linear expansion, to prevent moving of the optical modulation element, and to maintain a constant temperature and a uniform in-plane temperature distribution of the optical modulation element.
On the other hand, if the dust-preventing member is made of metal, it is possible to improve the heat dissipation effect. In particular, when a polarizer is bonded to the transparent plate, it is preferable that the dust-preventing member be made of metal because heat is generated with the absorption of light by the polarizer.